Plastic jackets, and also reinforced plastic jackets or covers, are usually made by feeding two webs of plastic foil material to a seaming machine; the foils are then welded at weld seams along immediately adjacent edges. Covers for ring binders and the like are made in a similar manner; stiff inserts, for example of cardboard material or the like, are inserted between the foils which, then, are welded together by surrounding weld seams. At predetermined bend or fold or crease lines, additional weld seams can be formed, extending for example generally between longitudinal edges of the seamed foils, to form predetermined bend or fold zones or "living hinges".
Machines are used to form the jackets, whether reinforced or not, to which the webs are supplied in form of long foils, rolled off from supply rolls. The machines use vertically reciprocating welding heads which are formed with welding and selectively with cutting edges, corresponding to the contour of the jackets or covers to be made. A heating arrangement is located in the machine frame or in a base opposite the welding head which is used to plasticize the foils in the region of the weld head, which may be formed, additionally, with cutting edges. The foils are plasticized or made tacky or partially liquefied, so that the desired intimate weld connection between the foils is obtained. At the same time, knife-like cutting edges can form the desired outline during the welding process.
There is a danger that the foil will adhere to the heated base upon plasticizing the foil with heat. Usually, therefore, a separating foil is inserted between the heating arrangement and the foils to be actually worked on. This separating layer, usually, is an elongated web or foil itself, of a material which prevents undesired adhesion and tacking of the foils to be welded with the machine base or the Weld base.
Heat-welding of this type, in which a heater is used has a disadvantage in that the heat is derived only from one side. During the welding process, and within the overlapping foils, this leads to a substantial temperature gradient. Consequently, the side of the foil adjacent the heating structure is heated to a substantially higher extent, and will be more softened or plasticized than the side adjacent the welding head or welding punch portion.
The foil may also be plasticized in a different manner, and, as well known, by subjecting it to high-frequency radiation. This method, however, can be used only with foils which have a poor electrical loss angle. High frequency passes through other foils, without heating the foils. Polyolefins, for example polypropylene, are often preferred due to environmental considerations, and such material cannot be handled by high-frequency heating apparatus.
Apparatus to manufacture foils, and particularly reinforced foils or similar articles, from elongated foil webs have another problem, namely the resulting scrap. Usually, the welding heads or welding stamps, together with the cutting edges on the welding heads, are the image of the weld seams and the cut edges of the finished product. The result is scrap having the appearance of a rope ladder, which is obtained when the products are separated out from the web. This rope ladder-like scrap is difficult to handle.